Strong association but no correlation. Exercise 14.19 (page 305)

gives these data on the speed (miles per hour) and mileage (miles per gallon)

of a car:

Speed: 30 40 50 60 70 Mileage: 20 24 26 24 20 The least-squares line for predicting mileage from speed is mileage = 22.8 + (0 × speed)

Chapter 15 Exercises 331

(a) Make a scatterplot of the data and draw this line on the plot.

(b) The correlation between mileage and speed is r = 0. What does this say about the usefulness of the regression line in predicting mileage?